Leaching Trench Field


Leaching trenches are the oldest form of existing practices for discharging wastewater to the soil. Standard leaching trenches use gravity to discharge the wastewater into a series of lines of perforated pipe embedded in gravel.

Septic Tanks Overview

The function of septic tanks in septic systems are to hold back the solid wastes and move on the wastewater. These are normally concrete tanks in the ground which may or may not contain separated compartments. Septic tanks are often crucial part in a septic design. Septic system designs often site septic tanks based first on the local concrete manufacturer. Often times, the capacity of the septic tank sited is dependent on which manufacturer is used. Some manufacturers have longer wait times to manufacturer specific septic tank capacities.

concrete septic tank being collapsed, note separate chambers

Some septic tanks are made of alternate materials other than concrete, including polyethylene or fiberglass. Some benefits to utilizing these alternate materials is that they are lightweight and can be carried easier with a chain and a small excavator machine. Some septic tanks are so lightweight they can be lifted with several people.

yellow polyethylene septic tank

The water from septic tanks is sometimes called septic effluent. The term septic itself means without oxygen and septic effluent is composed mostly of bacteria and human feces. It is a highly contaminated liquid and human contact is dangerous. Septic tank effluent contains particles of sewage of size 1/16 to 3/16 inch in diameter. The waste strength is measure in Biological Oxygen Demand or BOD.

septic effluent

The function of septic tanks in septic systems are to hold back the solid wastes and move on the wastewater.

Options for Leaching Trench Field Installation

Gravelless Chambers/Products

More and more residential wastewater products are hitting the market that are some form of gravelless product. A gravelless product is an of the shelf method of distributing wastewater for an onsite wastewater treatment system.

Gravel can be substituted with gravelless chambers or engineered gravelless pipe. The main function of the gravel is to create void space and allow for the distribution of the wastewater. The chambers function is to similarly create void space allowing for wastewater to discharge.

Gravelless products eliminate the need for using gravel. Gravelless products can make installation quicker and are also convenient for difficult sites such as steep slopes which make hauling gravel difficult.

Gravel Trenches

Gravel is inexpensive and readily available. It is the common media choice for distributing wastewater to trenches.

Options for Distribution

Sequential Distribution

Sequential distribution in leaching trenches works by first filling up the first trench and then on to the next trench in the sequence. This configuration results in one distribution box per leaching trench.

Note each distribution box is one trench

This is a good option if you are on a sloping site with some fall.

Parallel Distribution

Parallel distribution in leaching trenches works by first filling up a distribution box which is meant to distribute the water evenly between all trenches in the system.

note all the feeder lines off of the distribution box

This is a good option if the area you are distributing to is flat.

Labor of Septic System Installation

Any new installation of a septic system requires planning, installation, and regulatory oversight.


Septic system planning involves soil scientists and septic system designers. Both of these are often separate private contractors and require a fee and visits to the property. Often, these contractors possess a highly specialized knowledge base and are in high demand. Septic Designers require knowledge in local regulations, soil analysis, septic system types and their product and design considerations. Often times, engineers and surveyors just do not possess a knowledge of local products, system regulation requirements to make completing design plans economical due to the high variability in regulations and products available between locations.


Septic systems, because they can pose health risks when not installed or function properly, by law must have regulatory agencies, commonly your local public health department oversee the design and installation. The regulators often will require a fee through the cost of permit and or site review and multiple visits to the property.

Installation Contractors

Septic systems require an expert contractor and often require contractors to become registered with each county they work in. Septic system installers require often large earth moving equipment, the ability to dig sometimes deep holes for tank placement, moving large amounts or sand, gravel, and soil. Knowledge of local regulations and the ability to follow design plans and work with designers. Often, local contractors will be dealers or distributors of particular types of septic system products. This can be either an additional revenue or they can get discounts from the manufacturers by buying said products in bulk and making those their main septic system products used in installations.

Service Contractors

Septic systems require periodic maintenance...some much more than others. A general method of determining the maintenance required is to count up all the mechanical components of a system. The septic tank to Sand Pressure Mound has one mechanical component...the pump system. The Spray Distribution System has 3 mechanical components depending on the type of pretreatment system used...the aeration motor, the ultraviolet light, the pump system. Each mechanical component is wired to an alarm and when it fails, triggers the alarm.

Many modern systems are required by law for the owner to maintain a service contract with a service provider. Your local health department often requires service provider companies to register. You can call the local health department to get a list of service providers. When calling contractors, sometimes it helps to have the manufacturer name and system name to get prices. Most new systems come with a 2 year warranty.
System operation costs vary depending on the system. After conducting baseline research on most system types, the annual operation of most onsite and discharging systems, with service contracts, the cost is equatable to what you would pay annually for city sewer bills.